Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $92.34   4.553%   $96.5442   $96.54   $96.55   $96.50  
  Purchase #2 $46.63   4.145%   $48.5628   $48.56   $48.55   $48.60  
  Purchase #3 $17.65   13.540%   $20.0398   $20.04   $20.05   $20.00  
  Purchase #4 $197.88   12.694%   $222.9989   $223.00   $223.00   $223.00  
  Purchase #5 $178.89   13.273%   $202.6341   $202.63   $202.65   $202.60  
  Purchase #6 $138.94   4.192%   $144.7644   $144.76   $144.75   $144.80  
  Purchase #7 $18.39   10.753%   $20.3675   $20.37   $20.35   $20.40  
  7 purchase totals = $690.72       $755.9117   $755.90   $755.90   $755.90